When light is projected to specific molecules, inelastic scattering occurs between light and the molecules in the probability of 1/1,000,000 and the light partially loses its energy by the constituents and structures of the molecules to cause a variation in wavelength. The Raman spectroscopy is developed to obtain information about constituents and structures of target molecules, using such a mechanism, i.e., by projecting a mono-wavelength laser and by analyzing the intensity of reflected light (Raman signal) in wavelength bands. The Raman spectroscopy is nowadays rising as the new-generation analyzing technology by virtue of its rapidness, accuracy, and capability of nondestructive analysis.
However, as the Raman spectroscopy makes inelastic scattering occur in very low probability of 1/1,000,000, intensity of reflected light is very weak. Therefore, if an amount of molecules to be analyzed is minutely little, the Raman spectroscopy is regarded as being unsuitable for inspecting trace materials because an obtained Raman signal cannot be differentiated from a background signal.
To solve such low signal intensity, there has been proposed a methodological technique using an effect of Surface-Enhanced Raman Scattering (SERS). The SERS is the technology of increasing a Raman signal, which is obtained from molecules absorbed on a nanostructured surface, 103 to 1,015 times by greatly increasing intensity of light by locally focusing the projected light through a Surface Plasmon Resonance (SPR) effect of the nanostructured surface such as Au or Ag.
Nanostructures utilizing such an SERS effect may be generally disposed on a plane substrate. Nanostructures may be manufactured in a form of SERS substrate to perform an analysis by laser after spreading trace molecules, which are to be analyzed, on the surface of the substrate through a suitable process such as drop casting. An SERS substrate should be high in signal enhancement effect to allow an analysis of trace molecules, superior in signal equality and reproducibility due to a high uniformity rate of nanostructures on the substrate, and inexpensive in manufacturing cost because of difficult recycling.
General SERS substrates have been manufactured, roughly, in two methods. One is using a photolithography process such as photolithography or E-beam lithography to form a pattern and to deposit Au or Ag for nanostructures, accomplishing topological uniformity, but disadvantageous with a high price of lithography equipment for pattering and with a high processing cost thereof. The other one is compounding nanostructures into a solution and then scattering the solution on a substrate to manufacture an SERS substrate, having a simple and inexpensive process, but disadvantageous with remarkably low signal equality and reproducibility because the nanostructures are randomly distributed on the substrate.
Therefore, to widely utilizing the Raman spectroscopy using SERS in analyzing trace molecules, there is a need of technology for manufacturing an SERS substrate having high signal enhancement capability, superior signal equality and reproducibility, and low manufacturing cost.